Bricker, who had been at Allegiant for more than 10 years, oversaw most of the airline’s key functions, including what routes the airline flew, how much it charged for tickets, and how it bought airplanes. He told colleagues he planned to spend the summer with his family. Scott Sheldon, Allegiant’s CFO, will temporarily handle the COO job.

Bricker became COO in 2016 after his predecessor, Steve Harfst, resigned, effective immediately. Then, as now, Allegiant gave no explanation.

Under Bricker, Allegiant expanded the types of routes it few, adding flights from larger cities, such as Cincinnati, Memphis and Austin. It also bought new airplanes for the first time in its history, placing an order last year for 12 new Airbus A320s. The first was delivered in mid-May.

Bricker is the latest in a series higher-profile defections. He left two weeks after the airline’s chief marketing officer, Ponder Harrison, who said he couldn’t keep working at Allegiant due to family needs. Harrison had been an executive at Allegiant from 2002 to 2009, but he had only rejoined the company in March. In departing, Harrison said in a statement that he was not ready to move to Nevada, where the airline is based.

In an email, Allegiant spokeswoman Hilarie Grey said it did not make sense to group the two recent executive departures together. “Ponder was a completely different circumstance,” she said.